1. Field of Invention
This invention relates to a control system for an internal combustion engine equipped with a variable valve timing device hydraulically driven for selectively advancing or retarding an opening and closing timing of an intake valve.
2. Description of Related Art
Conventionally, in an internal combustion engine (ICE) equipped with a variable valve timing (VVT) device for adjusting an opening and closing timing of an intake valve, the VVT may be used to facilitate startup by performing a decompression operation (DECOMP). In a decompression operation, the cylinder pressure during cranking is suppressed, which helps create a stable or smooth start up of the ICE with reduced vibration. For example, an existing technology used in a hybrid electric vehicle automatically stops and restarts an ICE to save fuel when the vehicle stops at intersections or crossings, and during such restarts, the VVT retards the variable valve timing to a prescribed retarded position (a decompression operation).
When the valve timing is greatly retarded in an ICE during a decompression operation, the charging efficiency of the engine becomes low, and thus an undesirable result may be that the torque generated by the engine is suppressed. Accordingly, it is desirable to advance the VVT device to an original advanced position when the engine is started by a cranking operation. In particular, to ensure acceleration performance, for example to provide a sufficient level of starting acceleration performance in a HEV from the engine auto-stop condition to the auto-start condition in response to the gas pedal being pressed suddenly, an immediate start of control to advance the VVT device is desirable.